Transformer Based Voltage Supply
There is disclosed a voltage summer including a transformer having a primary side and a secondary side, wherein a first voltage to be summed is connected to the primary side and a second voltage to be summed is connected to the secondary side. There is further disclosed a transformer comprising a primary winding and a secondary winding and having a turns ratio of primary winding to secondary winding of x:y, providing x turns in series in the primary winding and providing y turns in series in the secondary winding; providing an equal number of turns in the primary and secondary windings; and closely coupling each primary winding turn with a secondary winding turn.
Latest NUJIRA LTD. Patents:
The present invention relates to the provision of a voltage. The invention is concerned particularly, but not exclusively, with the provision of a supply voltage to a power amplifier, in an arrangement in which the supply voltage may be selectable. The invention is particularly but not exclusively concerned with the control of a supply voltage to an amplifier such as a broadband radio frequency (RF) amplifier having a wide dynamic range.
BACKGROUND TO THE INVENTIONTransistor amplifiers have a peak efficiency for a particular input power that is a function of geometry (i.e. circuit components and layout), load and supply voltage. In conventional radio frequency (RF) power amplification these characteristics are fixed based on the peak input level expected. For amplifiers presented with an input signal having a wide dynamic range, the input signal infrequently achieves peak levels and frequently operates below peak levels. As such, the amplifier may exhibit low overall efficiency.
A solution to the problem of low amplifier efficiency is to vary one or more of the above-stated characteristics (geometry, load, supply voltage) in response to the input signal. Techniques to vary one or more of these characteristics are known in the art.
Techniques that vary the device geometry and load tend to be very dependent on the particular power amplifier topology used, and generally present challenging RF problems. Repeatability of such designs in production is generally a problem.
Various techniques are known in the art for enhancing amplifier efficiency based on the supply voltage. Of supply voltage based efficiency enhancement schemes, there are two broad classifications of solution. These solutions are:
(i) envelope elimination and restoration, and
(ii) envelope tracking.
Envelope elimination and restoration requires the amplifier to be driven saturated, and all the envelope information to be applied through the amplifier supply. This technique tends to be generally too demanding upon the supply modulator when using high modulation bandwidths, and thus has limited usefulness in practical applications.
With envelope tracking, the amplifier is driven in a substantially linear fashion. Envelope tracking requires an efficient power supply capable of delivering high modulation power bandwidths. In known techniques, a switched mode pulse width modulator (commonly referred to as class S) is used to realise an efficient variable supply to the power amplifier. However, in order to operate at full bandwidth, the supply must switch at many times the bandwidth of the modulation, and this excessively high switching speed results in poor modulator efficiency.
In another prior art envelope tracking technique, a plurality of highly efficient intermediate power supplies are provided, and the power supplies are switched as required by the envelope level. This switching creates transient disturbances that degrade the spectrum with high order intermodulation products, and makes linearisation difficult by introducing supply dependent non-linearities alongside input dependent non-linearities.
In a further modification to this technique, the switching of the power supplies is combined with a linear amplifier to provide a smooth transition between switch levels and remove the supply dependent linearisation requirement. The aim of this form of envelope tracking is to provide a unique value of supply voltage for every envelope level. However, there is a problem in achieving this without impact upon tracking speed capability.
A variable level power supply must be able to switch between different supply levels in order to provide the necessary varied voltage supply levels. One known method of achieving this is to provide a means of coarse switching between a number of voltage sources, However this course switching results in errors in the voltage supply signal, as illustrated in
However, in practice, using coarse switching, the power supply envelope follows a shape as represented by the stepped curve 104. In the example illustrated with reference to
In order to address this problem, it is known to sum the selected coarse voltage with a finely adjustable voltage source in order to provide interpolation, and to minimise the error.
A particularly advantageous technique for controlling the selection of the supply voltage, and adjustments thereto, to improve efficiency is taught in British patent application number 0303826.2.
It is an aim of the present invention to provide an improved scheme for summing voltages in the generation of a supply voltage.
SUMMARY OF THE INVENTIONAccording to one aspect of the invention there is provided a voltage summer including a transformer having a primary side and a secondary side, wherein a first voltage to be summed is connected to the primary side and a second voltage to be summed is connected to the secondary side.
The first voltage may be connected between the first tap of the primary side and the second tap of the primary side, and the second voltage is connected to a first tap of the secondary side, a summed voltage being provided on a second tap of the primary or secondary side.
The first voltage may be greater than the second voltage and the summed voltage is provided on the second tap of the primary side of the transformer.
The first voltage may be a variable voltage. The first voltage may be provided by a switchable voltage source. The second voltage may be variable. The second voltage may be provided by a switchable voltage source.
The first voltage may be variable between n levels and the second voltage is variable between m levels, wherein the summed voltage is variable between n*m levels.
The second voltage may be provided by a continuously variable voltage source.
The first voltage signal may be a coarse voltage signal and the second voltage signal may be a fine voltage signal. The fine voltage signal may be representative of an error in the course voltage signal.
The voltage summer may further include a reference voltage source, and a difference means for removing the reference voltage from the summed voltage to generate the second voltage.
The voltage summer may further include a reference current source, a means for sensing the current in the primary side of the transformer, a difference means for removing the reference current from the sensed current to generate a difference current, and a driver for supplying the second voltage in dependence on the difference current.
A power supply preferably includes a voltage summer as defined. The power supply is preferably for driving a power amplifier, preferably an RF power amplifier.
In a further aspect, the invention provides a method of summing voltages including applying a first voltage to a primary side of a transformer and applying a second voltage to a secondary side of the transformer, wherein a sum of the first and second voltages is provided on one of the first or second sides of the transformer.
A method according to claim 15, wherein the first voltage is applied between the first tap of the primary side and the second tap of the primary side, and the second voltage is applied to a first tap of the secondary side, wherein a summed voltage is provided on a second tap of the primary or secondary side.
The first voltage may be greater than the second voltage and the summed voltage may be provided on the second tap of the primary side of the transformer.
The method according to any one of claims 15 to 17 further comprising the step of varying the first voltage. The method may further comprise the step of varying the second voltage. The method may comprise varying the first voltage between n levels and varying the second voltage between m levels, wherein the summed voltage is thereby variable between n*m levels.
The first voltage signal may be a coarse voltage signal and the second voltage signal may be a fine voltage signal. The fine voltage signal may be representative of an error in the course voltage signal.
The method may further include the step of generating a reference voltage, and removing the reference voltage from the summed voltage to thereby generate the second voltage.
The method may further include the step of generating a reference current, sensing the current in the primary side of the transformer, removing the reference current from the sensed current to generate a difference current, and supplying the second voltage in dependence on the difference current.
In a further aspect, the invention provides a transformer comprising a primary winding and a secondary winding and having a turns ratio of primary winding to secondary winding of x:y, the transformer including: x turns in series in the primary winding and y turns in series in the secondary winding; an equal number of turns in the primary and secondary windings. each primary winding turn closely coupled with a secondary winding turn.
The closely coupled turns are preferably coupled in parallel. The number of turns in the primary and secondary winding is preferably x*y. There is preferably provided y parallel branches in the primary winding, each with x turns.
There is preferably provided x parallel branches in the secondary winding, each with y turns.
There is preferably provided z branches in the primary winding, the number of turns in the primary winding being z*x*y. There may be provided z*x/y branches in the secondary winding. There may be an equal number of turns in each parallel branch. The number of branches in the primary winding may be y*z, the number of branches in the secondary winding being x*z.
There may be provided a plurality of primary windings i each having a turns ratio of primary winding to secondary winding of xi:y, wherein each turn of each primary winding is closely coupled with a turn of each other primary winding.
The number of turns in the primary and secondary winding may be the lowest common multiple of xi*y for all i.
The lowest common multiple may be t, the number of branches in each primary winding being t/xi, and each having xi turns. The number of branches in the secondary winding may be t/y, each having y turns.
There may be provided pi branches in each primary winding, the number of turns in each primary winding being pi*xi*y.
In a further aspect there is provided a transformer comprising a plurality i of primary windings and a secondary winding and having a turns ratio of primary winding to secondary winding of xi:y, the transformer including: x; turns in series in each primary winding i and y turns in series in the secondary winding; an equal number of turns in each primary and secondary windings; and each primary winding turn being closely coupled with a turn of every other primary winding and with a secondary winding turn. Such transformer may thereby be used to sum a plurality of voltages.
BRIEF DESCRIPTION OF THE DRAWINGSThe present invention in now described by way of example with reference to the accompanying Figures, in which:—
The present invention is described herein by way of particular examples and specifically with reference to a preferred embodiment. It will be understood by one skilled in the art that the invention is not limited to the details of the specific embodiments given herein. In an embodiment the invention is described herein by way of reference to the provision of a power supply for an RF amplification stage. However more generally the invention may apply to any arrangement where it is necessary to switch between a plurality of voltage supplies in order to provide a modulatable power supply.
It should be noted that where the same reference numerals are used in different Figures, they refer to the same elements.
Referring to
The transformer 206 has a secondary side generally designated by reference numeral 209, and a primary side generally designated by reference numeral 208. The primary side 208 has a first connection point or tap 210, and a second connection point or tap 214. The secondary side has a first connection point or tap 212, and a second connection point or tap 216.
The switchable main voltage source 202 receives a plurality m of DC voltages on lines 2281 to 228m from respective DC voltage sources 2301 to 230m. The switchable main voltage source 202 is controlled, by means not shown but understood by one skilled in the art, to switch one of the plurality m voltages at its inputs to its output on line 224.
The fine correction voltage source 204 provides an alternating voltage signal on an output line 226, to correct errors in the voltage signal provided on the output line 224 of the switchable main voltage source 202. The correction voltage generated on line 226 by the fine correction voltage source 204 is summed with the selected output voltage on line 224 to correct or minimise any error therein.
In accordance with the principles of the invention, the summing operation is performed by the transformer 206. The selected output voltage on the output line 224 of the switchable main voltage source 202 is connected to the first tap 212 of the secondary side 209 of the transformer 206. The fine correction voltage on line 226 is connected to the first tap 210 of the primary side 208 of the transformer 206. The second tap 214 of the primary side 208 of the transformer 206 is connected via a line 218 to ground, which is represented by terminal 220. More generally, it can be considered that the fine correction voltage is applied across the taps of the primary side of the transformer. The second tap 216 of the secondary side 209 of the transformer 206 is connected to a line 222 which provides the output voltage supply. Thus, the output voltage supply on line 222 corresponds to the selected voltage provided on line 224, suitably adjusted by the fine correction voltage on line 226.
In an alternative, the switchable main voltage may be applied across the taps of the primary side of the transformer, and the fine correction voltage applied to the first tap 212 of the secondary side.
The power supply arrangement illustrated in
As illustrated in
In a further embodiment, the fine correction voltage source 204 may be replaced by a switched highly efficient voltage source, which is switched independent of the switching in the switchable main voltage source 202. Such an adaptation of the arrangement of
As illustrated in
The arrangement of
A further embodiment incorporating the principles of the invention is illustrated with respect to
As mentioned above, use of the transformer 206 provides a loss-less technique for summing the main voltage source with the correction voltage source. As illustrated by the various embodiments of FIGS. 2 to 4, the correction voltage source may be provided in a number of ways. The invention is not limited to any particular technique for generating either the main (coarse) voltage source or the correction (fine) voltage source. Either the main voltage source or the correction voltage source could be a combination of switches and resistive or reactive interpolation means in order to provide the necessary accuracy demanded by a particular application. The invention is thus not limited to the specific implementations for generating the main voltage source or correction voltage source illustrated with reference to FIGS. 2 to 4.
In implementing the principles of the embodiments of the invention illustrated in relation to the embodiments of FIGS. 2 to 4, it can be seen that the broad principle is the use of a transformer to sum two voltages. Specific construction of the transformer may vary. The principle relies upon one voltage being connected to the primary side of the transformer, and the other voltage being connected to the secondary side of the transformer.
In delivering a power supply, a power supply means may be applied to one side of the transformer, and the power supply for driving a device, preferably a power amplifier, delivered by the other side of the transformer.
In a preferred embodiment the transformer is implemented with a larger number of turns on the primary side 208 than on the secondary side 209. This allows for smaller and faster electronic devices to be used in the switch or amplifier circuits connected to the primary side of the transformer, such that the voltages are isolated.
In all embodiments, if the transformer 206 uses a ferromagnetic material for the transformer core, DC current flowing through the core may magnetise the core, and this may result in saturation of the core with a consequent loss of magnetising inductance. In order to overcome this potential problem, in an embodiment a DC current is applied to the primary side 208 of the transformer 206 in such a manner that the magnetic field strength (H) in the primary side 208 cancels the magnetic field strength in the secondary side 209.
This DC current may be applied, in the embodiment of
A further embodiment utilising the principles of the present invention is illustrated in
The embodiment of the invention illustrated in
The arrangement of
An alternative implementation of the feedback correction technique of
Referring to
The arrangement of
Thus, as described hereinabove with reference to various embodiments, embodiments of the invention provides a technique in which a transformer is used to add two supply voltages. In the various embodiments, the two supply voltages added are a main supply voltage and a correction voltage. More generally, these may be considered to be a coarse voltage and a fine voltage. Thus a voltage source having a coarse representation of the desired output voltage, but containing errors which are alternating in nature, is corrected by a voltage source having a fine representation of these errors. The thus corrected voltage source provides an output power supply voltage, which may be used as required in any given implementation. The embodiments have particular advantages when used as a wide bandwidth modulatable power supply, particularly for providing a power supply to a power amplifier.
When used as a wide bandwidth modulatable power supply, it is necessary for the transformer to have a very wide bandwidth. This is particularly the case when the correction of the supply voltage is achieved by feedback through the transformer, as illustrated in the embodiments of
At high frequencies, the performance of some conventional transformers may be restricted. This is because, with some conventional transformers, leakage inductance restricts the high frequency response to the transformer, and hence the bandwidth. The leakage inductance can be overcome by implementing the transformer in a transmission line configuration. However, this is not an appropriate use of the transformer in order to sum voltages, as discussed in the various embodiments hereinabove, since the summing of the voltages in an efficient manner requires the primary and secondary sides of the transformer to be isolated. The isolation is key to achieving loss-less summation of voltages. Thus, the conventional technique for minimising leakage induction, using the transmission line configuration, is not an option.
Thus, in an embodiment of the invention, an adapted transformer is used for the summation of the voltages.
It is proposed that the transformer is adapted in order to maximise the coupling between primary and secondary windings, preferably through use of bifilar or twisted-pair windings. Leakage inductance which is a result of flux lines that do not link between the windings of the transformer through the core are therefore reduced.
Preferably each turn of a primary winding should form one half of the twisted pair, the other half being formed by the secondary winding. In the case of a step down transformer, for example, there will be more primary turns than secondary turns. In order to satisfy the close coupling requirement, in a step down transformer secondary turns are therefore connected in parallel.
In order to reduce leakage inductance, the concept of parallel turns may be extended still further. If the windings are connected in parallel, then the self-inductance of the windings is reduced by a factor equal to the number of windings connected in parallel. However, since the winding fluxes link through the core, the mutual inductance between windings means the combined inductance of a winding is independent of the number of turns wound in parallel.
Since leakage inductance is formed as a result of flux linkages that fail to link through the core, this mutual inductance does not exist for leakage inductance. This means that leakage inductance is reduced by a factor equal to the number of turns connected in parallel, but the magnetising inductance remains constant.
Referring to
The example is of a primary side of the transformer consisting of two windings of three turns, the two windings connected in parallel. Reference numerals 51, 53, 55 form one winding, and reference numerals 57, 59, 61 form a second winding.
The secondary windings consist of six single turns, all connected in parallel.
The primary and secondary windings are preferably bifilar wound together. A transformer wound in such a manner as shown in
As mentioned hereinabove, the example of
The principles of embodiment of
Thus, in this aspect of the invention, the principle is to provide for each winding, on either side of the transformer a complimentary winding, and to closely couple such windings on the core. This may require additional windings to be provided than would otherwise be required, on either the primary or the secondary side, but ensures that leakage inductance is reduced.
The general principles of the construction of the adapted transformer are set-out as follows, for a transformer having a given ratio of x:y from primary to secondary, where x is the number of turns on the primary winding and y is the number of turns on the secondary winding.
The overall number of turns in the primary and secondary winding must be equal. In order to ensure that the number of turns in each winding is equal, a general principle is that each winding should have x*y turns.
Each turn of the primary winding is coupled with a turn of the secondary winding. The coupled turns are then wound in a closely coupled fashion, or bonded.
Where additional turns are added in order to ensure that the total number of turns in each side is x*y, additional turns may need to be connected in parallel branches. Where parallel branches are provided, there must be an equal number of series turns in each of the parallel branches. This applies to parallel branches in the primary side or in the secondary side.
Where a plurality of branches p is provided in the primary side, the total number of turns in each side of the transformer is p*x*y. Where p branches are provided in the primary winding, the total number of secondary branches connected in parallel is p*x/y.
It is possible that p*x/y may become fractional. In such case, it is necessary to factor p*x/y into integer values. The term p is therefore multiplied by the denominator value such that p*x/y becomes an integer. In this way, the principles for adapting the transformer may be scaled to any turns ratio transformer.
In the simple case described hereinabove with reference to
In the example of
As a result of the primary winding having p branches, the secondary winding must have p*x/y secondary branches connected in parallel. This is calculated to be six secondary branches. As the secondary winding must also have six (p*x*y) turns, then the secondary winding is constructed to have six branches of one turn each, all connected in parallel.
The exemplary transformer described hereinabove with reference to
In a scenario where N signals are summed, an N-filar winding is preferably used. N windings would then be closely coupled together. The conditions for operation described hereinabove in the two signal summation case must still be met, and each individual turn of each winding must be closely coupled together.
In the case where there are w signals to be summed, w independent primary windings are provided. Each of the w independent primary winding has a respective number of turns x. Each x*y product is found for each independent winding, and then the lowest common multiple found. For example, for a 3:2:1 transformer the x*y products are 3 (for the 3:1 winding) and 2 (for the 2:1 winding). The lowest common multiple in such case, for respective ratios of 2 and 3, is 6. In general, this lowest common multiple may be denoted as t.
For each winding, there then must be t total turns. In this example, this requires each winding to have 6 turns. This require both the independent primary winding to have 6 turns, and the secondary winding to have six turns. The total number of branches in each primary winding is thus t/x, for the x value for the respective independent primary winding. Thus in the example above, for the primary winding with 3 turns 2 branches are required, and for the primary winding with 2 turns 3 branches are required. The branches of the primary windings must be connected in parallel to maintain the transformer ratios.
The total number of secondary turns in the secondary winding must also be t, and the number of secondary parallel branches must be t/y. As in the above example y=1, then the number of secondary parallel branches is 6.
As discussed above, each parallel branch in any winding must contain an equal number of turns.
In a further modification, any of the independent primary windings may be provided with multiple branches. For example, any primary winding may have p branches, such as discussed hereinabove with reference to
An embodiment for the summing of multiple signals by the provision of multiple primary winding is considered further herein below. As discussed above, a first primary winding denoted w1 has three turns, and two branches, each with three turns. Thus for the first primary winding x1=3 and p1=2. A second primary winding w2 has two turns and one branch. Thus for the second primary winding x2=2 and p2=1. In order to achieve the desired ratios of 3:1 for the first primary winding and 2:1 for the second primary winding, the second primary winding is required to have one winding of one turn.
The lowest common multiple t is (p1*x1*y)*(p2*x2*y), which in the example is twelve. Thus t=12, and there is a requirement for each primary winding and the secondary winding to have twelve turns.
In the first primary winding, the number of parallel branches now required is t/x1, i.e. four. In the second primary winding, the number of parallel branches now required is t/x2, i.e. six. In the secondary winding the number of parallel branches required is t/y, i.e. twelve.
In general, there may be provided a plurality of primary windings wi, each having a number of turns xi in a branch.
In the example of utilising a transformer having multiple primary windings in order to sum multiple signals, the primary signals are all summed together with the voltage that is applied to the input side of the secondary winding.
In an alternative arrangement, multiple secondary windings may be provided. In such case, there may be reciprocal coupling across all the primaries. For this reason, one of the primary windings may be a voltage source, but the remaining primary windings must be current sources to avoid loading the windings.
The present invention has been described herein by way of reference to particular preferred embodiments. However the invention is not limited to such embodiments. The present invention has particular application in relation to RF amplifiers, but is not limited to such implementation. The invention can be advantageously utilised in any environment where switched, selectable voltage supplies are provided.
The described preferred embodiments utilising an RF amplifier are not limited to any particular load being driven by such RF amplifier. However it is envisaged that such an RF amplifier will typically drive an antenna. As such, the present invention has particularly advantageous uses in the field of communications, including the field of mobile communications.
Claims
1. A voltage summer including a transformer having a primary side and a secondary side, wherein a first voltage to be summed is connected to the primary side and a second voltage to be summed is connected to the secondary side.
2. A voltage summer according to claim 1, wherein the first voltage is connected between the first tap of the primary side and the second tap of the primary side, and the second voltage is connected to a first tap of the secondary side, a summed voltage being provided on a second tap of the primary or secondary side.
3. A voltage summer according to claim 2, wherein the first voltage is greater than the second voltage and the summed voltage is provided on the second tap of the primary side of the transformer.
4. A voltage summer according to claim 1 wherein the first voltage is a variable voltage.
5. A voltage summer according to claim 4 wherein the first voltage is provided by a first switchable voltage source.
6. A voltage summer according to claim 4 wherein the second voltage is variable.
7. A voltage summer according to claim 6 wherein the second voltage is provided by a second switchable voltage source.
8. A voltage summer according to claim 6 wherein the first voltage is variable between n levels and the second voltage is variable between m levels, wherein the summed voltage is variable between n*m levels.
9. A voltage summer according to claim 6 wherein the second voltage is provided by a continuously variable voltage source.
10. A voltage summer according to claim 6 wherein the second voltage is provided by a fixed voltage source.
11. A voltage source according to claim 1 wherein the first voltage is a coarse voltage signal and the second voltage is a fine voltage signal.
12. A voltage source according to claim 11 wherein the fine voltage signal is representative of an error in the course voltage signal.
13. A voltage summer according to claim 12, further including a reference voltage source, and a difference means for removing the reference voltage from the summed voltage to generate the second voltage.
14. A voltage summer according to claim 12, further including a reference current source, a means for sensing the current in the primary side of the transformer, a difference means for removing the reference current from the sensed current to generate a difference current, and a driver for supplying the second voltage in dependence on the difference current.
15. (canceled)
16. A method of summing voltages including applying a first voltage to a primary side of a transformer and applying a second voltage to a secondary side of the transformer, wherein a sum of the first and second voltages is provided on one of the first or second sides of the transformer.
17. A method according to claim 16, wherein the first voltage is applied between the first tap of the primary side and the second tap of the primary side, and the second voltage is applied to a first tap of the secondary side, wherein a summed voltage is provided on a second tap of the primary or secondary side.
18. A method according to claim 17, wherein the first voltage is greater than the second voltage and the summed voltage is provided on the second tap of the primary side of the transformer.
19. A method according to claim 16 further comprising the step of varying the first voltage.
20. A method according to claim 16 further comprising the step of varying the second voltage.
21. A method according to claim 19 comprising varying the first voltage between n levels and varying the second voltage between m levels, wherein the summed voltage is thereby variable between n*m levels.
22. A method according to claim 16 wherein the first voltage is a coarse voltage signal and the second voltage is a fine voltage signal.
23. A method according to claim 22 wherein the fine voltage signal is representative of an error in the course voltage signal.
24. A method according to claim 16, further including the step of generating a reference voltage, and removing the reference voltage from the summed voltage to thereby generate the second voltage.
25. A method according to claim 16, further including the step of generating a reference current, sensing the current in the primary side of the transformer, removing the reference current from the sensed current to generate a difference current, and supplying the second voltage in dependence on the difference current.
26. A transformer comprising a primary winding and a secondary winding and having a turns ratio of primary winding to secondary winding of x:y, the transformer including:
- a. x turns in series in the primary winding and y turns in series in the secondary winding;
- b. an equal number of turns in the primary and secondary windings; and
- c. each primary winding turn closely coupled with a secondary winding turn.
27. (canceled)
28. A transformer according to claim 26 wherein the number of turns in each of the primary and secondary winding is x*y.
29. A transformer according to claim 28 wherein there is provided y parallel branches in the primary winding, each with x turns.
30. A transformer according to claim 28, wherein there is provided x parallel branches in the secondary winding, each with y turns.
31. A transformer according to claim 28, wherein there is provided p branches in the primary winding, the number of turns in the primary winding being p*x*y.
32. A transformer according to claim 31 wherein there is provided p*x branches in the secondary winding.
33. A transformer according to claim 28 wherein there is an equal number of turns in each parallel branch.
34. A transformer according to claim 31 wherein the number of branches in the primary winding is y*p, the number of branches in the secondary winding being x*p.
35. A transformer according to claim 31 in which there is provided a plurality of primary windings i each having a turns ratio of primary winding to secondary winding of xi:y, wherein each turn of each primary winding is closely coupled with a turn of each other primary winding.
36. A transformer according to claim 35 in which the umber of terms in the primary and secondary winding is the lowest common multiple of xi*y for all i.
37. A transformer according to claim 36 in which the lowest common multiple is t, the number of branches in each primary winding being t/xi, each having xi turns.
38. A transformer according to claim 37 in which the number of branches in the secondary winding is t/y, each having y turns.
39. A transformer according to claim 35, wherein there is provide pi branches in each primary winding, the number of turns in each primary winding being pi*xi*y.
40. A transformer comprising a plurality i of primary windings and a secondary winding and having a turns ratio of primary winding to secondary winding of xi:y, the transformer including:
- a. xi turns in series in each primary winding i and y turns in series in the secondary winding;
- b. an equal number of turns in each primary and secondary windings; and
- c. each primary winding turn being closely coupled a turn of every other primary winding and with a secondary winding turn.
Type: Application
Filed: Dec 7, 2004
Publication Date: Dec 6, 2007
Patent Grant number: 7764060
Applicant: NUJIRA LTD. (Cambridge CB3 7TA)
Inventor: Martin Wilson (Holmdel, NJ)
Application Number: 10/596,301
International Classification: G05F 1/14 (20060101); H01F 27/28 (20060101);